See also this particular post from the results I listed: Getting checksum error while installing Rocky Linux 8 from generated ISO from original ISO - #6 by nazunalika
It lists the tools being used, not only extract, but for recreating after. Since plenty of people have experienced problems making custom ISO’s, and the issue has already been addressed on the forums, read the results to see if it helps 
Here’s another: Custom Rocky ISO for Post Production - #2 by nazunalika using livemedia-creator with a link as well to how it’s being used for Rocky ISO’s.
If none of those results help, you’ll have to wait until someone else jumps in on the thread.